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Old Jan 30th 2009, 10:33 PM   #1
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Vector-Change in velocity

Hi everyone

Just a tad confused:
An ice-skater moving at 20m/s turns right through an angle of 60 degrees while maintaining the same speed. What is the magnitude of her change in velocity?

The confusing part is how do I draw the triangle to represent this information?

Thanks in advance for your help
Steven
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Old Jan 30th 2009, 10:47 PM   #2
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Originally Posted by stevoevo22 View Post
Hi everyone

Just a tad confused:
An ice-skater moving at 20m/s turns right through an angle of 60 degrees while maintaining the same speed. What is the magnitude of her change in velocity?

The confusing part is how do I draw the triangle to represent this information?

Thanks in advance for your help
Steven
A triangle ABC, angle A equals 60 degrees, and AB=AC=60, BC would be the change in velocity. You can use cosine law to find your answer.
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Old Jan 30th 2009, 10:53 PM   #3
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Thanks, that's easy enough (as it is an equilaterla triangle) even though I didn't realise it...

Thanks heaps
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Old Jan 30th 2009, 10:57 PM   #4
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Actually just one more thing...

Why is the angle 60 degrees, shouldn't it be 120?
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Old Jan 31st 2009, 12:19 AM   #5
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Originally Posted by stevoevo22 View Post
Actually just one more thing...

Why is the angle 60 degrees, shouldn't it be 120?
Welcome steven
Which angle are you talking about?
Are you confused why the triangle is equilateral.
It is given that the speed remains same which means the two angles opposite them in the triangle are equal. Now its given that an angle is 60 degree. Then the sum of the other two angles which are equal must be 120 degree. So each must be 60 degree.
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Old Jan 31st 2009, 02:40 AM   #6
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Thanks for the welcome
Actually I would like to change that question, because I am no longer confused about that.

Instead, I would really like an explanation in simple terms of how the 3rd side of the triangle represents the change in velocity. I understand what the change in velocity is, but I don't understand how this line represents it.
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Old Feb 4th 2009, 04:12 AM   #7
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In simle terms I cannot explain it for velocity but for displacement. See its like this. Suppose you travel 3 m east and then turn 90 degree towards south and travel 4 m (please draw a figure for better understanding). Your displacement (change in position) can be given as the line from your initial position to your final position. This becomes the third side of the triangle. For a right angled triangle you can compute it easily using pythagoras theore. In this case your displacement is 5 m.
Similarly you can apply it for velocity. Hope you understood.
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